1. Field of the Invention
The present invention relates to a liquid crystal display and a manufacturing method thereof.
2. Discussion of the Related Art
A liquid crystal display is capable of displaying desired images by adjusting the intensity of an electric field created in a liquid crystal material having an anisotropic dielectric constant and injected between upper and lower transparent insulating substrates. The electric field changes the molecular arrangement of the liquid crystal material and thereby adjusts the amount of light passing through the transparent insulating substrates. A thin film transistor substrate (TFT LCD) employing thin film transistors (TFTs) as switching elements is used in the liquid crystal display.
The liquid crystal display includes a liquid crystal panel having a plurality of pixels defined by gate lines and data lines to display images and a driving circuit unit for driving the liquid crystal panel.
The driving circuit unit includes gate drivers and source drivers for driving the gate lines and data lines, respectively, of the liquid crystal panel, a timing controller for controlling driving timing of the gate drivers and source drivers, and a power source for supplying driving voltages needed to drive the liquid crystal panel and driving circuit unit.
The gate drivers and source drivers may be implemented in a number of integrated circuits (ICs). The ICs may be mounted using a tape carrier package (TCP), a chip-on-film (COF) structure where it is mounted on a base film of the tape carrier package and then is coupled electrically to the liquid crystal in a TAP (tape automated bonding) method, a chip-on-glass (COG) structure where it is mounted directly on the liquid crystal, and the like.
FIGS. 1 and 2 are schematic illustrations of a liquid crystal display according to the related art, wherein FIG. 1 shows a structure generally used for laptop computers and FIG. 2 shows a chip-on-glass (COG)-type cascade structure.
In the liquid crystal display having the structure shown FIG. 1, video data and control signals (gate control signal and data control signal) output from a timing controller 132 and driving voltages (reference power source) output from a power source 131 are all applied to each source driver 121 or each gate driver 111 via signal lines in a T-bone structure arranged on a printed circuit board (PCB) 130.
The timing controller 132 and power source 131 are chips that are mounted on the printed circuit board 130, and the gate drivers 111 and source drivers 121 are mounted on the tape carrier packages 110, 120, respectively, and connected to the liquid crystal panel 100.
The source drivers 121 are supplied with data control signals and video data from the timing controller 132 mounted on the printed circuit board 130 and driving voltages from the power source 131 through the tape carrier package 120, respectively, and the gate drivers 111 are supplied with gate control signals and driving voltages from the timing controller 132 and power source 131 through the tape carrier package 110.
This structure inevitably requires a printed circuit board 130 having a large area to apply signals to the source drivers 121 and gate drivers 111. Even when replaced by a chip-on-glass structure by bonding the source drivers 121 or gate drivers 111 to the exterior of the liquid crystal panel 100, a large area printed circuit board 130 will still be required.
On the other hand, in a liquid crystal display having the structure shown FIG. 2, the source drivers 121 and gate drivers 111 are mounted on the liquid crystal panel 100 using a chip-on-glass configuration. The source drivers 121 and gate drivers 111 are also supplied with control signals, video data, and driving voltages from the timing controller 132 and power source 131 on the printed circuit board 130 through a flexible print circuit (FPC) 140 and the line-on-glass (LOG)-type signal lines formed on the liquid crystal panel 100.
Because the gate drivers 111 receive relatively a small number of signals in comparison with the source drivers 121, it is also possible to arrange the signal lines on the liquid crystal panel using a line on glass configuration without providing a separate printed circuit board for supplying signals to the gate drivers 11.
In this structure, driving signals and control signals necessarily pass through the FPC board 140 so that they may be supplied to the gate drivers 111 and source drivers 121 bonded on the liquid crystal 100. This structure has the following problems.
First, the two-step process of chip-on-glass bonding and flexible printed circuit board manufacturing leads to the increase of the number of processes and requisite materials.
Second, the increase of the line-on-glass resistance, inner wiring resistance of the chip on glass, and bonding resistance causes the increase of output deviations and the image quality's deterioration.
Finally, the rise of material cost due to the application of the flexible printed circuit board is another problem with the two-step process.